Color picture tube with rectangular hall shadow mask

ABSTRACT

A cathode-ray tube for displaying colored images comprises an in-line three-element gun and a shadow mask. The shadow mask has formed therein a plurality of rectangular holes arranged in an orderly manner in rows and columns. The dimensions and spacing of the rectangular holes is selected to provide for optimum transmission of the electron beams to the screen, while still providing mechanical strength for the shadow mask.

United States Patent Inventor Akiyoshi Kouno Tokyo, Japan Appl. No. 4,620 Filed Jan. 21, 1970 Patented Jan. 4, 1972 Assignee Nippon Electric Company, Limited Tokyo, Japan Priority Jan. 24, 1969 Japan 44/5159.

COLOR PICTURE TUBE WITH RECTANGULAR HALL SHADOW MASK 4 Claims, 2 Drawing Figs.

US. Cl 313/2 B, 3 13/85 S Int. Cl. ..H0lj 29/32,

[50] Field of Search 3 l 3/85 S, 82 NC, 92 B, 92

[56] References Cited FOREIGN PATENTS 598,821 5/1970 Canada 313/85 S 1,112,542 8/1961 Germany 313/85 S Primary Examiner-Robert Segal Attomey-Sandoo, Hopgood and Calimafde AISTRACT: A cathode-ray tube for displaying colored images comprises an in-line three-element gun and a shadow mask. The shadow mask has formed therein a plurality of rectangular holes arranged in an orderly manner in rows and columns. The dimensions and spacing of the rectangular holes is selected to provide for optimum transmission of the electron beams to the screen, while still providing mechanical strength 3 for the shadow mask.

COLOR PICTURE TUBE WlTI-I RECTANGULAR HALL SHADOW MASK This invention relates to cathode-ray tubes for displaying colored television images, and in particular, to cathode-ray tubes with a combination of an in-line gun of the three electron beam type and a shadow mask of the rectangular hole type.

The conventional cathode-ray tubes for displaying color television images, includes an electron gun system that conventionally emits three separate electron beams, a display screen on the inner surface of a displaying part of the tube envelope commonly containing three luminescent substances, and an apertured metal mask located a small distance from the display screen and having many holes or slots through which the electron beams strike the luminescent substances to emit light. These three components of the tube are not independent, but rather the design of each component is largely interdependent to that of the others.

The most representative tubes utilize a combination of an electron gun system that is composed of three separate electron guns located at the vertices of regular triangles, and a metal mask of the shadow mask type having a large number of small circular holes. The display screen is composed of a large number of small luminescent dots, three different dots being provided for each hole in the shadow mask. These three different dots are arranged at the vertices of regular triangles, very similar to that of the electron guns, and upon excitation by electron beams emit light of different colors, usually red, green and blue. Since each electron beam is assigned for each of the three colors, each electron beam must strike the corresponding color dots over the entire display screen to reproduce high-quality color images. Since the display screen and the shadow mask are at the same electric potential, and the luminescent dots are so orderly arranged with reference to the holes of the shadow mask; if the three electron beams are always converged on the shadow mask, precise alignment of electron beams and luminescent dots is possible. At present, however, such convergence is very difficult to achieve by static means, so-called static convergence; and a means for applying time-varying convergence signal, the so-called dynamic convergence, is required to accomplish the precise convergence. When the electron beams of triangular arrangement are used, this convergence is very complex and difficult to adjust.

Another possible arrangement of electron beams is the one in which the three electron beams are arranged along the socalled in-line beams. When the in-line electron beams are used, the dynamic convergence for the direction perpendicular to the line on which the electron beams are aligned can be eliminated. Further, since the two outside electron beams are usually located symmetrically with respect to the central electron beam, dynamic convergence is considerably simplified from that for the triangular electron beams. Also, the design of the shadow mask is simplified since the electron beams are injected through the shadow mask holes on the same plane, and only the pitch distribution of the shadow mask holes along the direction of electron beam alignment satisfies the complex geometrical relationship among the spacing between the display screen and the shadow mask, the electron beam spacing at the deflection center and others. Further, the design and arrangement of the shadow mask holes are more flexible than those for the triangular beam type tubes without a sacrifice in picture quality.

The representative color tubes with the in-line electron gun that emits in-line electron beams utilize shadow masks consisting of parallel wires or having narrow parallel slots, so-called shadow grill, in order to utilize all possible merits of utilizing in-line electron beams, However, shadow masks having a grilled structure are weak in mechanical strength, and the effects of thermal expansion due to the collisions of electron beams on the mask are very severe. These difficulties usually limit the shape of the shadow grill to a cylindrical shape rather than a spherical shape for most shadow masks. This cylindrical shape and the thermal effects limit the shadow grill for use only in color tubes having a small display screen.

The conventional shadow masks with circular holes can be used with the in-line electron guns. However, they intercept much more of the electron beams than the shadow grill and are as a result poorer in color brightness. The conventional shadow mask minimizes the merits of utilizing the in-line electron gun in a cathode-ray tube for displaying a colored images.

It is, therefore, the broad object of this invention to provide a cathode-ray tube for displaying colored image by combining an in-line electron gun and a shadow mask of a new design to utilize all the aforementioned merits of the in-line electron beams, shadow mask and shadow grill.

It is a more specific object of the invention to provide a shadow mask in a cathode-ray tube for achieving the broad objective.

In accordance with the invention, the cathode-ray tube for displaying colored images comprises a shadow mask with a large number of small rectangular holes, located at a small distance from the display screen. The screen contains three times as many of small rectangular luminescent dots as there are holes in the mask. The rectangular holes are aligned in rows and columns. The row is parallel to the line on which the three electron beams emitted from an in-line electron gun are aligned, and the wide side of the rectangular hole is parallel to the column. The wide side of the rectangular hole is slightly shorter than the spacing between the rows, but the location of the rectangular holes in every other row is shifted to the right or ,left as much as a half of the spacing between the rectangular holes in the row, which is slightly larger than three times the narrow side of the rectangular hole. Therefore, the rectangular holes in neighboring rows are not aligned in a column, but the rectangular holes in every other row are exactly aligned in column. The rectangular luminescent dots on the display screen are arranged exactly "the same way as the shadow mask, but include three rectangular luminescent dots of about the same size as the rectangular hole per each rectangular holes. The central dots of three rectangular luminescent dots is located exactly behind the rectangular hole in the mask and other two dots are located on each side of the central dots in a row. These three dots are composed of different luminescent materials so that when they are hit by the electron beam, they emit different colors, usually blue, red and green. Therefore, the display screen is almost completely filled with the rectangular luminescent dots, but the dots are each completely separated by very small gaps. Because of the rectangular shape of the shadow mask holes and of their arrangement, the transmission factor of the electron beams through the shadow mask is equal to that of the shadow grill, but the shadow mask is strong enough mechanically and can be formed on a spherical surface. Further, since none of the neighboring luminescent dots is of the same color, the image on the screen is substantially structureless. Therefore, this invention provides brighter and clearer color images, ease of converging electron beams, and does not place a practical limit on screen sizes.

These and other objects and advantages, the nature of the present invention and its various features, will appear more fully upon consideration of the illustrative embodiment now to be described in detail in connection with the accompanying drawings, in which:

FIG. 1 is a diagrammatic longitudinal section taken through a cathode-ray tube in accordance with the invention;

FIG. 2 is a fragmentary view on an enlarged scale of the structure of a shadow mask for use in the tube shown in FIG. 1.

FIG. 1, included for purpose of explanation, is a considerably simplified diagrammatic longitudinal section of a cathode-ra tube taken along the surface on which three in-line electron beams are aligned. In the figure, a display screen is coated on the inner surface of a faceplate l, which is supported by a glass funnel 2. A shadow mask 3, through which the in-line electron beams 4 strike the display screen, is located at a small distance from the face 1. The display screen comprises a large number of three kinds of orderly arranged rectangular dots and luminesce difi'erently when they are impinged by electron beams 4, namely red, green and blue. The electric potential of these dots is kept exactly the same as that of the shadow mask 3. The shape of the faceplate 1 is spherical as the most representative television tubes are. The shape of the shadow mask 3 is also spherical.

FIG. 2 is an enlarged part of the shadow mask 3 that is the most important part of this invention. The holes 5 of the shadow mask are rectangular in shape, and are spaced almost equally by a distance along the same direction as the in-line electron beams are aligned, this line hereinafter being designated as a mask hole row. The mask hole rows 6 are spaced by a distance b along the direction perpendicular to the row. The ratio b:a must be larger than 0.34:1, but smaller than 1511. To eliminate any possibility of an electron beam striking more than one luminescent dot simultaneously, the wide side 7 of the rectangular hole must be smaller than b, and the narrow side 8 must be smaller than a/3. Further, the wide side 7 of the rectangular hole 5 is perpendicular to the line along which the in-line electron beams are aligned. This arrangement allows the rectangular hole 5 to maintain as large as possible hole area even when the hole spacing a is decreased.

The hole spacing a must be determined so as to satisfy the geometrical relationship among the distance between the display screen and the shadow mask, the electron beam spacings at the deflection center, and others, since the mask hole row 6 is aligned with the in-line electron beams, The row spacing b is arbitrarily chosen in this case, because the in-line electron beams are used.

In this invention, however, the row spacing is restricted from the aforementioned restriction of 0.34:1 b:a l5:l This is to maintain the rectangular shape for the mask hole 5 to secure mechanical strength and at the same time to maximize the electron beam transmission factor, and to secure substantially structureless picture images.

in order to avoid an electron beam striking more than one luminescent dots simultaneously, there are provided guard bands between the luminescent dots. These guard bands decrease unavoidably the effective area of the mask hole, and hence decrease the electron beam transmission factor. When the mask hole is circular in shape as for the conventional shadow mask, the electron beam transmission factor decreases inversely proportional to the square of the width of the guard band. On the other hand, the electron beam transmission factor of the rectangular hole, such as in this invention, decreases proportionally to the ratio between the narrow side and the wide side of the rectangular hole. Therefore, the amount of decrease of the electron beam transmission factor is smaller for the rectangular hole even if the same guard band is provided for both the circular and rectangular structures. In a cathode-ray tube for displaying colored images, in which the metal mask similar to the shadow mask has a different electric potential than the display screen, the rectangular hole has to be modified to avoid the distortion in the electron beam trajectory and the top and bottom sides have to be curved. This shape is poor in electron beam transmission similarly to the circular shape when b/a is closer to 0.34/l. in this invention, it is not necessary to round the top and bottom side of the rectangular hole, rather it is better to have square comers as much as practical etching technique permits.

Further making this invention clear, the arrangement of the luminescent dots on the display screen in described. As shown in FIG. 2, the location of the rectangular holes 5 in every other row is shifted from that of the neighboring rows by as much as a half of the hole spacing a. Therefore, the rectangular holes in immediately neighboring rows are not aligned in a column, but the rectangular holes in every other row are exactly aligned in a column. The arrangement of luminescent dots is obviously determined from the arrangement of the shadow mask holes. The luminescent dots are rectangular in shape, and are about the same size as the rectangular holes. The dots for green luminescence are usually located immediately behind the rectangular holes,'and the red and blue dots are arranged at both sides of the green dot, facing the wide sides of the rectangular hole directly ad acent each other and separated by a narrow gap. Sets of three luminescent dots, red (R), green (G) and blue (B), are located in a row as R.G.B. R.G.B. for example. This arrangement is very similar to that of FIG. 2, but red and blue dots are filling between the rectangular holes. Therefore, all neighboring luminescent dots in both rows and columns are different in color.

For a further illustration of the invention, the following details are given of a shadow mask providing highly satisfactory images with simple control.

A large number of cathode-ray tubes having a spherical faceplate of 19 in. in diagonal dimension were built in accordance with the invention. Representative dimensions of the shadows masks used were 0.15 mm. in thickness, 0.18 mm. X 2.4 mm. in rectangular hole size, a=0.8 mm. and b=2.5 mm. The shadow mask was placed about 10 mm. from the display screen. The electron gun used was an in-line gun of a singlelens system.

As repeatedly mentioned in the explanation, the shadow mask in accordance with the invention is maintained at the same electric potential as the display screen, and it is used to provide the color selection only by the difference in the angles of the injecting electron beams through the rectangular holes. The shape of the holes is a rectangle with square comers as far as is practically achievable, in order to achieve the maximum possible transmission of electron beams through the holes. Since the rectangular slot of rounded shape is poorer in electron beam transmission, a convergence mask with rounded rectangular slots is different in principle and function, and it is obviously outside the objective of this invention.

What is claimed is:

l. A color cathode-ray tube comprising a shadow mask, an electron gun for producing three electron beams aligned on a straight line for convergence on said shadow mask, and a display screen comprising rectangular luminescent dots, said shadow mask having a plurality of orderly arranged rectangular holes formed therein in a plurality of rows and columns, said holes being spaced by a distance a in each of said rows, and by a distance b in each of said columns, the ratio b/a being larger than 0.34 but smaller than 15, said rectangular holes in every other of said rows being offset with respect to the holes in an adjacent row so that all adjacent rectangular dots on said display screen luminesce differently in color when struck by the electron beam from said electron gun passing through said shadow mask rectangular holes; each of said rectangular holes having a wide side dimension of less than b and a narrow side dimension of less than a/3; said wide side being perpendicular to the direction on which said three electron beams are aligned.

2. The cathode-ray tube of claim 1, in which the rectangular holes in immediately adjacent ones of said columns are not aligned, and the rectangular holes in every other one of said rows are arranged in aligned columns.

3. The cathode-ray tube of claim 2, in which said luminescent dots are substantially the same size as said rectangular holes in said shadow mask.

4. The cathode-ray tube of claim 3, in which said luminescent dots are arranged in groups of three, the central one of each of said groups of dots being located closely to and in registration with one of said rectangular holes.

i l k I t 

1. A color cathode-ray tube comprising a shadow mask, an electron gun for producing three electron beams aligned on a straight line for convergence on said shadow mask, and a display screen comprising rectangular luminescent dots, said shadow mask having a pluraliTy of orderly arranged rectangular holes formed therein in a plurality of rows and columns, said holes being spaced by a distance a in each of said rows, and by a distance b in each of said columns, the ratio b/a being larger than 0.34 but smaller than 15, said rectangular holes in every other of said rows being offset with respect to the holes in an adjacent row so that all adjacent rectangular dots on said display screen luminesce differently in color when struck by the electron beam from said electron gun passing through said shadow mask rectangular holes; each of said rectangular holes having a wide side dimension of less than b and a narrow side dimension of less than a/3; said wide side being perpendicular to the direction on which said three electron beams are aligned.
 2. The cathode-ray tube of claim 1, in which the rectangular holes in immediately adjacent ones of said columns are not aligned, and the rectangular holes in every other one of said rows are arranged in aligned columns.
 3. The cathode-ray tube of claim 2, in which said luminescent dots are substantially the same size as said rectangular holes in said shadow mask.
 4. The cathode-ray tube of claim 3, in which said luminescent dots are arranged in groups of three, the central one of each of said groups of dots being located closely to and in registration with one of said rectangular holes. 